The present invention relates to a working cycle for a heat engine, especially an internal combustion engine.
Heat engines, e.g. internal combustion engines of the reciprocating piston type, have been used extensively for a long time for driving a wide range of machinery, both stationary, e.g. generators, pumps, and compressors, and movable, e.g. land, sea, and aerial vehicles. In the technology of internal combustion engines the two principal working cycles are the Otto cycle and the Diesel cycle. Both these cycles have been used in both two- and four-stroke variants.
In heat engines of the type referred to above, the principal, ideal working cycle includes isentropic compression of the gas, isochoric addition of heat to the gas, isentropic expansion of the gas, and isochoric return of the gas to its condition at the start of the working cycle.
This ideal cycle is only possible under certain conditions, i.e. the working medium is an ideal gas having constant specific heats cp, cv, there are no heat, gas or flow losses, the addition and dissipation of heat is instantaneous, and there is no residual gas.
In the internal combustion engine technology it is desirable to achieve as high efficiency as possible, and this is true for both the mechanical and the thermal efficiency. There are many reasons for this, and among these there is a desire to reduce the fuel consumption of the engine, and thereby to reduce the operation costs, and also a desire to reduce the emission of harmful residues from the combustion to the environment.
One way to increase the thermal efficiency of an internal combustion engine is, as can be seen above, to raise the compression ratio of the engine. However, there are certain limitations to this, because a high compression ratio gives a high pressure in the combustion chamber in the cylinder or cylinders of the engine at the end of the compression. During combustion, the stresses of the engine, especially the moving parts, then become very high. In order to get sufficient strength, the dimensions of the parts have to be increased, which means increased weight and increased internal friction and lowers the mechanical efficiency. High pressures also lead to problems regarding control of the ignition of the fuel, and this is particularly the case for spark ignition engines, i.e. engines working according to the Otto working cycle, but also compression ignition engines, i.e. engines working according to the Diesel working cycle, will encounter problems if the pressure in the combustion chamber is very high at the end of the compression.
An object of the present invention is to provide a working cycle for a heat engine, said working cycle enabling an increase in the thermal efficiency of the engine in comparison to previously known heat engines.
Another object of the present invention is to provide a working cycle for an internal combustion engine of the reciprocating piston type, said working cycle enabling an increase of the thermal efficiency of the engine in comparison to a conventional engine, said working cycle being applicable to both spark ignition and compression ignition engines of both two- and four-stroke types.
This is achieved by a working cycle as defined above.
Another object of the present invention is to provide an internal combustion engine having increased thermal efficiency compared to a conventional engine, said engine of the present invention being either a spark ignition or a compression ignition engine of the two- or four-stroke type.
This is achieved by an internal combustion engine of the initially defined type.
Preferable embodiments of the working cycle and the engine are defined in the depending claims.